This is only a contribution of how to configure spamassassin to score mails with a reply-to header that is different from the sender (From: header). This is usually a technique used by spammers but often some real users are using this functionality. Be careful, make sure to not get in troubles yourself by implementing this rule, before using it!!!

Notice that the scored points in this guide are very high, you can setting as you need it. In my case I make the decision of send to quarantine almost all mails using a reply-to because it's what I needed, maybe it's a good stuff setting down a low score like 0.001 to get started and see if this is what you need!

Rule FromNotReplyTo. Score 2 points to mail with reply-to and from headers are not the sameRule FromNotReplyToSameDomain. Score 5 points to mail with reply-to and from headers are not in the same domain

################### Add in /etc/mail/spamassassin/local.conf ##################### Score 2 points to mail with reply-to and from headers are not the sameloadplugin FromNotReplyTo plugins/FromNotReplyTo.pmheader FROM_NOT_REPLYTO eval:check_for_from_not_reply_to()score FROM_NOT_REPLYTO 2.0describe FROM_NOT_REPLYTO From: does not match Reply-To:

# Score 5 points to mail with reply-to and from headers are not the same domainloadplugin FromNotReplyToSameDomain plugins/FromNotReplyToSameDomain.pmheader FROM_NOT_REPLYTO_SAME_DOMAIN eval:check_for_from_not_reply_to_same_domain()score FROM_NOT_REPLYTO_SAME_DOMAIN 5.0describe FROM_NOT_REPLYTO_SAME_DOMAIN From domain: does not match Reply-To: domain###########################################################################